1. Field of the Invention
The present invention generally relates to a semiconductor processing apparatus, and specifically to a plasma CVD apparatus having a self-cleaning device.
2. Description of the Related Art
Traditionally, CVD apparatuses have been used to deposit insulation film made of silicon oxide, silicon nitride, amorphous carbon or polymers containing benzene rings, conductive film made of tungsten silicide, titanium nitride or aluminum alloy, or high dielectric constant film containing PZT (PbZr1−xTixO3), BST (BaxSr1−xTiO3) or the like, on silicon substrates or glass substrates.
To deposit these films, reaction gas or secondary reaction gas, of various compositions, is supplied to the reactor. When plasma energy is applied, the reaction gas causes chemical reaction and forms a desired thin film on a semiconductor substrate. The film resulting from the reaction also attaches to the interior walls of the reactor and the surface of the susceptor. When the film deposition process is repeated on many substrates, these attachments also accumulate and eventually separate from the reactor walls/susceptor surface to float inside the reactor. The floating material becomes a source of impurities and contaminants that cause defects in the produced semiconductor circuits.
“In-situ cleaning,” which is a process of cleaning the interior of the reactor while the reactor is operating, is an effective way to remove the contaminants attached to the interior walls of the reactor. Under this method, cleaning gas selected in accordance with the type of attachment is introduced to the reactor to gasify and thereby remove the attachments. For example, CF4, C2F6 or NF3 is used as cleaning gas, among others, if the attached material is silicon oxide or nitride, or tungsten or its nitride or silicide. In this case, active species containing fluorine atoms or fluorine (fluorine radicals) gasify the attachments on the interior walls of the reactor and remove impurities.
On a plasma CVD apparatus, directly utilizing the plasma excitation device used for film deposition to activate cleaning gas causes the electrodes to receive large ion bombardments due to the large high-frequency power applied to the cleaning gas. As a result, the electrode surface is damaged and the surface layer separates, thus generating impurities and contaminants. The damaged electrodes must be replaced frequently, which causes the running cost to increase.
To resolve the problem of ion bombardments, a method called “remote plasma cleaning” was developed. Japanese Patent Laid-open No. 10-149989, Japanese Patent Laid-open No. 10-163185, and U.S. Pat. No. 5,788,778, for example, disclose the method to use NF3 as cleaning gas and activate the cleaning gas using microwaves inside a second plasma discharge chamber away from the reactor.
According to the above publications, NF3 is introduced to an isolated second plasma discharge chamber at a controlled flow rate, and then dissociated and activated by the 2.45 GHz microwaves supplied to the plasma discharge chamber via a waveguide from a microwave oscillator, to generate fluorine radicals. At this time, a pressure regulation valve provided between the second plasma reaction chamber and the reactor maintains the second plasma reaction chamber at a specified pressure, so that microwave plasma discharge occurs efficiently. Generated fluorine radicals are introduced via a conduit pipe into the reactor where film is deposited, to gasify and thereby remove the attachments on the interior walls of the reactor. Separately, U.S. Pat. No. 6,736,147 discloses an apparatus wherein a remote plasma discharge chamber and a reactor are connected by way of an aluminum pipe and a through-flow valve.
In the process of depositing thin film on wafers, generally film deposition gas is supplied uniformly over the entire wafer surface from a showerhead so that film is deposited uniformly over the entire wafer. This showerhead has many pores from which to supply the gas in a uniform manner. Installed above of the showerhead is a blocker plate used to straighten the flow of gas. This blocker plate serves to control and adjust in the section above the showerhead the flow of film deposition gas supplied from a gas supply pipe, in order to allow the film deposition gas to be supplied uniformly over the wafer from the showerhead. U.S. Pat. No. 5,935,334 discloses an apparatus having a blocker plate inside a showerhead. To adjust the gas flow, this blocker plate dams up the film deposition gas introduced from an introduction pipe, and then supplies the gas onto the top surface of the showerhead through multiple openings. As a result, the film deposition gas is supplied onto the wafer with sufficient uniformity.